docs: def cminus(a, b):
      '''
      cminus(a, b) returns the difference a - b as a numpy array object. Like numpy's subtract
        function or a - b syntax, minus will thread over the latest dimension possible.
      '''
      # adding/subtracting a constant to/from a sparse array is an error...
      spa = sps.issparse(a)
      spb = sps.issparse(b)
      if not spa: a = np.asarray(a)
      if not spb: b = np.asarray(b)
      if   spa: b = np.reshape(b, (1,1)) if len(np.shape(b)) == 0 else b
      elif spb: a = np.reshape(a, (1,1)) if len(np.shape(a)) == 0 else a
      return a - b